The value of x is 4
From the information given, if we assume that the segments that appear tangent are tangent, then, we have that, if from one external point, two tangents are drawn to a circle then they have equal tangent segments.
Tangent segment means line joining to the external point and the point of tangency.
Then, from the diagram shown, we can say that;
CB = CD
substitute the expressions
x + 3 = 7
collect like terms
x = 4